Abstract

BACKGROUND:

Visual masking paradigms assess the early part of visual information processing, which may reflect vulnerability measures for schizophrenia. We examined the neural substrates of visual backward performance in unaffected sibling of schizophrenia patients using functional magnetic resonance imaging (fMRI).

METHODS:

Twenty-one unaffected siblings of schizophrenia patients and 19 healthy controls performed a backward masking task and three functional localizer tasks to identify three visual processing regions of interest (ROI): lateral occipital complex (LO), the motion-sensitive area, and retinotopic areas. In the masking task, we systematically manipulated stimulus onset asynchronies (SOAs). We analyzed fMRI data in two complementary ways: 1) an ROI approach for three visual areas, and 2) a whole-brain analysis.

RESULTS:

The groups did not differ in behavioral performance. For ROI analysis, both groups increased activation as SOAs increased in LO. Groups did not differ in activation levels of the three ROIs. For whole-brain analysis, controls increased activation as a function of SOAs, compared with siblings in several regions (i.e., anterior cingulate cortex, posterior cingulate cortex, inferior prefrontal cortex, inferior parietal lobule).

CONCLUSIONS:

The study found: 1) area LO showed sensitivity to the masking effect in both groups; 2) siblings did not differ from controls in activation of LO; and 3) groups differed significantly in several brain regions outside visual processing areas that have been related to attentional or re-entrant processes. These findings suggest that LO dysfunction may be a disease indicator rather than a risk indicator for schizophrenia.

Copyright 2010 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

The beginning of each visual backward masking trial was signaled by two 100 ms flashes of a fixation point, followed by a 600-ms blank period. A target was briefly presented for 26.6 ms, followed by a 53.3-ms mask at one of the 4 possible SOAs (26.6, 40, 80, and 200 ms). After the mask disappeared, a blank screen was presented while subjects made responses. Since each trial lasted 5 seconds, there was a slight difference between the offset of a mask and the start of the next trial across trials depending on the SOA. On each trial, participants identified the location of a gap in a target (up, bottom, or left) by pressing a corresponding button with their dominant hand.

The mean (standard error, SE) performance of siblings and controls is shown for the 4 SOAs. Both groups showed increased accuracy with increasing SOAs (i.e., decreased masking effect) and the groups did not differ significantly at any SOA. Chance performance is 33% (indicated by a dotted line). Values are presented as mean (SE).

These figures show the time series of percent signal change for each region of interest in controls (the left panel) and siblings (the right panel). The abscissa reflects the time since target onset. A (controls) and B (siblings), Retinotopic areas. C (controls) and D (siblings), the human motion selective cortex (hMT+). E (controls) and F (siblings), the lateral occipital cortex (LO). Values are presented as mean (SE)

This figure shows the areas that controls showed increased activations compared with siblings from the exploratory whole brain analysis of regions that showed a parametric increase with increased SOAs (SOA 1,2 < SOA 3 < SOA 4). The coordinates of the regions are presented in .